Automatic starter for induction motors



fumi 24, 1930 J. soUsEDlK UTOMATISTARTER FOR INDUCTION MOTORS Filed Aug. 9, 1927 I Patented June 24, 1930 UNITED s'rATEs ,PATENT OFFICE JOSEF BOUSEDK, OF VSETIN, MOBAVIA, CZECHOSLOVAKIA AUTOIATIC STARTER FOB INDUCTION MOTORS Application Med August 9, 1927, Serial No. 211,777, and in Czechoslovakia September-6, 1928.

rlhis invention relates to an im roved automatic starter which enables in uction motors to be started by automatically cutting out, after the motor has started, the inductive Aresistance which opposes the current in the rotor winding, without contacts or the like having to be switched, so that this winding is so to speak short-circuited and merely acts as an ohmic resistance, vthe starter being of the t pe comprising a rotary ma netic body a Ording a magnetic flux path etween short-circuited coils and coils electricall connected with the rotor winding, the ormer and the latter coils beingl mounted on lsaid magnetic body.

The object of the resent'invention is to provide a starter of t e type above referred to which shall be more reliable and more eilicient than the starters of the same type as hitherto proposed.

The invention consists in an automatic starter for induction motors of the type above referred to in which the magnetic body is in the form of a casing having two sides and a connecting part between them, and centrifu ally operated cores of magnetic material mounted between the sides of the said casing, the coils referred to being in such relative positions with respect to thecores that, at the be innin of the starting operation, the dis aceab e cores cause the lines of force of t e coils connected to the rotor to be closed through the sides of the casing andthe said cores practically without passing through the short-circuit coils, whilst, as the speed increases, the said lines of force are closed-through the cores, the sides ofthe casing and the connecting part of the casing, at the same. time passing through the short-circuited coils.

One form of construction according to the invention is illustrated by way of example in the accompanying drawing where- 1n Figure 1 is a section of part of the motor through the axis when the motor is at rest, whilst igufre 2 is a section onthe line II-II 1n Fi ,ure 1, .l

igure 3 is a section of part 0f the motor through the axis when the motor is runniig, whilst igure 4 is a section on the line II-II in' Fi ure 3.

igure 5 is a diagram of the connections, a rotor with a two-phase winding being assumed in the constructional example selected.

Upon the shaft 10 of the rotor, the winding of which is denoted by R in Figure 5, is mounted fast a casing consisting of two parts 11 and 12. This casing is made of magnetizable metal, and carries two auxil-l iary coils 13 and 14, and also a short-circuited coil. 15. Between the coils are supported ring se ments 16, likewise of magnetizable material. These segments 16 may advantageously comprise a uide, so that they can move further away rom or nearer to the shaft 10. The guide may be obtained for exam le b means of a groove and tongue 1g. Yhe segments are pressed towards the shaft, by means for example of springs 18. When, however, the shaft 10 rotates, they move away'from it by centrifugal action.

The apparatus operates in the following Vhen the motor is switched into the circuit, it induces in the rotor winding R a current, which however cannot attain Aa dangerous strength, as the inductive resistance of the coils 13 and 14 comes into action. The lines of force of the magnetic field produced by the coils 13 and 14 are closed through the cores or segments 16, and extend substantially as indicated in Figure 1 by the dotted lines 19 and 20. The short-circuited coil 15 produces noeffect in this case.

The motor now starts running and the segments 16 move away from the shaft 10, until they reach the position shown in Figures 3 and 4. Here the lines of force are' indeed closed again through the segments 16, but in such a way that the short-circuited coil 15 is also included within their circuit, as indicated by the dotted line 21. The coils 13, 14 and 15 together now act as a short-circuited transformer, and the inductive resistance formed by R, 13 and 14 practically ceases to exist.

It is self-evident that instead of two coils 13 and 1d, several such coils may be employed. A similar remark applies to the coil 15. The choice of the number of these coils depends for example upon how many phases the rotor winding has.

T he casing 11, 12 preferably contains oil,

m which cools and insulates the coils 13, 14 and 15, and reduces the friction when the segments 16 move. 22 is a closure which shuts on" the filling aperture.

Having now described my invention,

what I claim as newv and desire to secure by Letters Patent is:-

An automatic starter for induction motors comprising a shaft, a. rotary magnetic body in the form of a casing having two g@ sides and an inner` connecting part mounted on the said shaft and annular recesses in the said sides, short-circuited coils mounted around the said inner connecting part, coils electrically connected with the rotor winding of the motor and mounted Within 'the said recesses in the sides of the rotary magnetic body and cores of ma netic material mounted between the said si es of the casing forming the rotary magnetic body, the said cores normally facing the said annular recesses and being capable of being displaced between 'the said sides under the action of centrifugal force, whereby at the beginning of the starting operation, the displaceable cores will cause the lines ot' force of the coils connected to the rotor Winding to be closed through the sides oi the casing and the said cores practically Without passing through the short-circuited 40 coils, Whilst as the speed increases and the cores move awaY from the said recesses towards the perip ery of the starter, the said lines of force are closed through the cores, the sides of the casing and the inner connecting part of the casing, at the same time passing through the short-circuited coils.

In testimony whereof I have signed my name to this specification.

JOSEF SOUSEDK. 

